The present invention relates to a turbine rotor disk fitted with blades having Christmastree-shaped roots.
More particularly, the invention relates to means enabling blades having Christmastree-shaped roots to be properly secured to the disk on which they are mounted, even at slow speeds of rotation.
With this method of fixing where the root of each blade is said to be xe2x80x9cChristmastree-shapedxe2x80x9d and is received in a complementary slot in the rotor disk on which the blades are mounted, it is necessary for rotation to be taking place at sufficient speed before centrifugal force ensures that no relative movement is possible. The teeth on the root of the blade do not bear properly against the corresponding grooves in a slot of the disk at low speeds, and a known remedy to this drawback is to provide a few setbacks, generally three setbacks, in the end face of the root to provide housings for receiving springs.
Each spring is constituted by a single curved strip placed in a setback: the ends of the strip are in the setback and the curved portion is directed outwardly, i.e. against the bottom of the corresponding slot in the rotor disk. Naturally, the depth of the setback is smaller than the deflection in the middle of the curved spring.
When the blades are mounted on the disk, the springs are placed in their setbacks and the Christmastree-shaped rotor of each blade is inserted into the corresponding slot of the disk, i.e. simultaneously with its three springs. This operation is very difficult and accidents often arise such as springs breaking or jamming.
An object of the present invention is to provide a turbine rotor disk fitted with blades having Christmastree-shaped roots, where the teeth of the blade roots are pressed against the complementary grooves formed in the slots of the disk by springs while avoiding the above-mentioned drawbacks of the prior art during assembly.
The invention thus provides a turbine rotor disk fitted with blades having Christmastree-shaped roots, said disk having complementary slots each receiving the root of a blade, wherein at least one stick having a setback holding a spring strip captive is placed in the bottom of each slot of the disk between said bottom and the end face of the root of the corresponding blade.
Advantageously, three of said sticks are disposed between the bottom of a slot in the disk and the end face of the root of the corresponding blade.
According to another characteristic, the end of the root of each blade has a rim against which one of said sticks comes into abutment.
The invention also provides a method of assembling a blade having a Christmastree-shaped root to a turbine rotor disk of the invention, the method comprising the following sequence of operations:
a) the rotor disk is placed so that its axis is in a horizontal position;
b) the slot of the disk in which the blade root is to be mounted is placed in the bottom position;
c) the blade is installed by slidably inserting the root of the blade in the slot of the disk; and
d) the stick(s) each fitted with a respective spring strip are then inserted into the empty space between the bottom of the slot in the disk and the end of the blade root until the first-inserted stick comes into abutment against said rim on the root of the blade.